1. Field of the Invention
The present invention relates to a magnetic recording medium having a concealment layer that conceals the color of the magnetic recording layer, and more particularly, to a card-like magnetic recording medium such as a credit card or bank cashing card. Moreover, the present invention also relates to a transferable magnetic recording medium used during the production of this type of magnetic recording medium by a transfer process.
The present application is based on Japanese Unexamined Patent Application, First Publication No. 2002-293067, and the contents of that application are incorporated in this specification.
2. Description of Related Art
Since magnetic recording media comprising the formation of a magnetic recording layer on a non-magnetic substratum have a brown or black magnetic recording layer attributable to the color of the magnetic particles in the magnetic recording layer, the region of this magnetic recording layer restricts the design of the recording medium and hinders the achieving of a high level of design properties. As a technique for imparting design properties to such magnetic recording media, a concealment layer is first layered on the magnetic recording layer so as to cover it in order to conceal the color of the magnetic recording layer with another color. Alternatively, a new pattern may be arranged on said concealment layer.
In order to satisfactorily conceal the magnetic recording layer, the concealment layer must completely conceal the color of the magnetic recording layer and must have satisfactory adhesion to the magnetic recording layer. In general, the concealment layer must also similarly have satisfactory adhesion to the portion of the non-magnetic substrate where the magnetic recording layer is not formed in addition to adhesion to the magnetic recording layer. Consequently, studies have been conducted so as to satisfy these conditions relating to concealment and adhesion of the concealment layer to the magnetic recording layer mainly by selecting a suitable blending design and binder resin for the magnetic recording layer or performing various types of treatment on the magnetic recording layer.
For example, the surface of the magnetic recording layer is normally laminated prior to forming the concealment layer, which together with enhancing the adhesive strength of the magnetic recording layer itself to the non-magnetic substrate, smoothens the surface of the magnetic recording layer to improve concealment of the magnetic recording layer by the concealment layer. When a magnetic recording layer is formed on a portion of the non-magnetic substrate in particular, a difference in level forms between the magnetic recording layer and the non-magnetic substrate, and since concealment of the magnetic recording layer by the concealment layer is impaired, the magnetic recording layer is embedded within the non-magnetic substrate followed by laminating of the surface of the magnetic recording layer so that the same level surface is formed between the surface of the magnetic recording layer and the surface of the non-magnetic substrate. The magnetic recording layer is required to have satisfactory processability in terms of heat resistance and so forth in order to realize satisfactory concealment in this manner.
However, designing the formulation of the magnetic recording layer requires that foremost considerations be given to the dispersion of magnetic particles involved in the output characteristics of the magnetic recording layer, and when a design is attempted to be implemented that simultaneously satisfies the aforementioned concealment, adhesion and heat resistance, this has been accompanied by difficulties depending on the magnetic particles used.
Recently, due to the growing demand for imparting more advanced design properties to magnetic cards, for example, multiple layers of concealment layers, pattern layers and so forth are layered onto the magnetic recording layer, resulting in the need to use magnetic particles having high output and high resolution to compensate for decreases in read-back output and resolution caused by increases in the total thickness of these non-magnetic layers.
Moreover, magnetic cards require the use of magnetic particles that satisfy the conditions of higher weather-resistant storage properties, environmental stability, and recorded information storage stability over a long period of time, and magnetoplumbite-type ferrite magnetic particles such as barium ferrite particles are frequently used for magnetic recording layers having high resistance to magnetic force (high coercivity), weather-resistant storage properties, high output and high resolution in order to accommodate these requirements.
However, the aforementioned magnetoplumbite-type ferrite magnetic particles have a larger particle size than conventional magnetic particles for magnetic recording layers, and since they are tabular, they stack easily during orientation treatment. Consequently, surface becomes rough, thereby decreasing the concealment by the concealment layer. In addition, the binder resin and magnetic particles of the magnetic recording layer are easily unevenly distributed resulting in inferior heat resistance. Moreover, holes easily form in the magnetic recording layer resulting in decreased film strength, and since coating solution for the concealment layer layered on the magnetic recording layer penetrates into the holes, concealment by the concealment layer decreases further.
In order to solve the problems accompanying this type of surface form and internal structure of the magnetic recording layer, Japanese Unexamined Patent Application, First Publication No. Hei 7-65356 enhances the strength, heat resistance, wear resistance and processability of a magnetic recording layer by providing a protective layer that covers it to reinforce the surface of the magnetic recording layer.
Therefore, a constitution was examined in which a concealment layer is layered onto an intermediate layer by using the aforementioned protective layer as an intermediate layer in order to retain its advantages.
The heat resistance during laminating is definitely improved by using a hard resin having a high Tg (glass transition point) for the intermediate layer that covers the magnetic recording layer. In addition, the concealment by the concealment layer is improved by smoothing the surface of the magnetic recording layer as a result of the intermediate layer covering any uneven surface. Moreover, the film strength as sequential layers is increased by layering sequentially an intermediate layer free of large holes onto the magnetic recording layer. Moreover, since holes in the magnetic recording layer are filled by the intermediate layer, concealment is improved without the concealment layer paint penetrating into the lower layer.
However, since a binder resin having a high Tg (glass transition point) is used for the intermediate layer based on the need to retain heat resistance, a difference occurs in thermal characteristics and dynamic characteristics between the card base and the intermediate layer, resulting in the formation of cracks at their boundary. As a result, coating solution for the concealment layer enters these cracks causing a decrease in concealment. In addition, since the dynamic characteristics of the coated layer vary considerably between the intermediate layer and concealment layer, adhesion between the two layers becomes poor.
On the other hand, although Japanese Unexamined Patent Application, First Publication No. Hei 7-25185 describes a method for ensuring adhesion between the magnetic recording layer and concealment layer by providing a thermal adhesive layer comprised of a vinyl acetate-vinyl chloride copolymer having a low Tg (glass transition point) between the magnetic recording layer and concealment layer, in this constitution, there is the possibility of the occurrence of sticking during laminating of the magnetic recording layer prior to forming the concealment layer. In addition, since the difference in level between the magnetic recording layer and non-magnetic substrate cannot be eliminated unless laminating is performed, concealment by the concealment layer decreases.
In this manner, magnetic recording media of the prior art had sometimes poor heat resistance or other poor processability depending on the magnetic particles used for the magnetic recording layer, and the concealment and adhesion of the concealment layer to the magnetic recording layer was sometimes impaired.